Proteolytic cleavage in an endolysosomal compartment is required for activation of Toll-like receptor 9.
Toll-like receptors (TLRs) activate the innate immune system in response to pathogens. Here we show that TLR9 proteolytic cleavage is a prerequisite for TLR9 signaling. Inhibition of lysosomal proteolysis rendered TLR9 inactive. The carboxy-terminal fragment of TLR9 thus generated included a portion of the TLR9 ectodomain, as well as the transmembrane and cytoplasmic domains. This cleavage fragment bound to the TLR9 ligand CpG DNA and, when expressed in Tlr9(-/-) dendritic cells, restored CpG DNA-induced cytokine production. Although cathepsin L generated the requisite TLR9 cleavage products in a cell-free in vitro system, several proteases influenced TLR9 cleavage in intact cells. Lysosomal proteolysis thus contributes to innate immunity by facilitating specific cleavage of TLR9.
Park
Boyoun
B
Whitehead Institute for Biomedical Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02115, USA.
Brinkmann
Melanie M
MM
Spooner
Eric
E
Lee
Clarissa C
CC
Kim
You-Me
YM
Ploegh
Hidde L
HL
D000818:Animals; D015153:Blotting, Western; D002403:Cathepsins / Q000276:immunology / Q000378:metabolism; D002460:Cell Line; D018899:CpG Islands; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation / Q000276:immunology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D007113:Immunity, Innate / Q000502:physiology*; D047468:Immunoprecipitation; D008247:Lysosomes / Q000276:immunology / Q000378:metabolism*; D008264:Macrophages / Q000187:drug effects / Q000276:immunology / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D021381:Protein Transport / Q000276:immunology; D015398:Signal Transduction / Q000276:immunology*; D051217:Toll-Like Receptor 9 / Q000235:genetics / Q000276:immunology / Q000378:metabolism*
D004791:Enzyme Inhibitors; D051217:Toll-Like Receptor 9; D002403:Cathepsins